Proportion. Box for sand. Box for gravel. ----------- --------------- ---------------- _Feet._ _Feet._ 1:1:2 1 by 1 1 by 2 1:1-1/2:3 1 by 1-1/2 1 by 3 1:2:4 1 by 2 2 by 2 1:2-1/2:5 1-1/4 by 2 2 by 2-1/2 1:3:5 1-1/2 by 2 2 by 2-1/2 1:3:6 1-1/2 by 2 2 by 3 A tight platform should be provided similar to that illustrated in Figure 12 upon which to mix the concrete. For mixing 1 or 2 bag batches a platform 9 by 10 feet will serve. DIRECTIONS FOR HAND MIXING. The mixing board should be located in convenient relation to the supply of materials and the work and should be level. The sand box is placed on the board, about 2 feet from one of the longer sides, and filled level with sand; the box is then lifted away and the sand spread in a 3 or 4 inch layer. The cement is spread as evenly as possible on' top of the sand. Two men with shovels, standing on opposite sides of the pile, turn the sand and cement in such a way that the materials axe thoroughly mixed. In turning the material it should not be simply dumped off the shovel, but should be shaken off the ends and sides, so that the two constituents will be mixed as they fall. The mass should be turned two or three times, or until it is of uniform color and there are no streaks of either sand or cement. A man with a hoe or rake may assist by raking the top over as the two men turn. When the sand-cement mixture is of a uniform color it should be spread out carefully in a layer and the gravel box placed on top. The box is filled with gravel and then removed, the gravel being spread over the sand-cement mixture. The mass is soaked with about one-half the quantity of water to be used, care being taken not to wash away any of the cement. The materials then should be turned over in much the same manner as was the sand-cement, except that instead of shaking them off the end of the shovel the whole load should be dumped and dragged back toward the mixer with the square end of the shovel. The wet gravel picks up the sand and cement as it rolls over when dragged back. The mixing should be continued until the mass is uniform, water being added to the dry spots during the mixing until the desired consistency is obtained. Experience counts considerably in mixing concrete with the least amount of labor; ordinarily three or four turnings are required to mix the materials thoroughly. After the final turning the concrete should be shoveled into a compact pile and then is ready for placing in the forms. PLACING. PLACING CONCRETE. The mixed concrete should be deposited in the forms within from 20 to 30 minutes from the time the water is added to the cement, as it begins to set or harden after this time. To disturb the concrete after the set has begun is risky, as it will lose some of its strength, the extent of the injury depending upon the seriousness of the disturbance.